Natural gas is transported over long distances in a gaseous state through onshore or offshore pipelines, or in a liquefied gas (LNG) state in an LNG carrier ship to a location of consumption. The LNG, which is obtained by cooling natural gas to a very low temperature (about −163° C.), takes up about 1/600 of the volume of the natural gas in a gaseous state, and is therefore highly suitable for marine transportation over long distances.
An LNG carrier designed to transport LNG across the sea and deliver the LNG to a location of consumption on land or an LNG regasification vessel (LNG RV) designed to transport the LNG across the sea to the location of consumption on land and regasify the LNG for use on land includes a storage tank (hereinafter, referred to as a cargo hold) which is capable of withstanding the cryogenic condition of the LNG.
If the vessel is rocked with a liquid cargo like LNG contained in the cargo hold, motion of the liquid occurs, resulting in sloshing impact on sidewalls and ceiling structures 21 and 22 of the cargo hold 20, as shown in FIG. 1. Due to this sloshing impact, components configuring the cargo hold such as a heat insulator and a barrier may be damaged.
Sloshing refers to the movement of liquid contained in the cargo hold induced by motion of a vessel or floating structure which occurs in various marine conditions. If only a portion of the inside of the cargo hold is filled with liquid, sloshing induced by the motion of the liquid may severely impact the walls and ceiling of the cargo hold, which is referred to as sloshing impact.
The sloshing phenomenon as above inevitably occurs due to motion of the vessel at sea, and the cargo hold should be designed to have a sufficient strength to withstand the sloshing load.
FIG. 2 is a cutaway perspective view illustrating a conventional cargo hold designed to prevent sloshing.
With reference to FIG. 2, a technique of forming an upper chamfer 31 and lower chamfer 32 at the upper and lower sides of a lateral side of the cargo hold 30 to be slanted at about 45° has been conventionally proposed to prevent sloshing. Forming chamfers at the cargo hold as above may distribute and attenuate sloshing load to an certain extent by changing the shape of the cargo hold.
However, the technique of forming chamfers at the cargo hold as in FIG. 2 is applicable only under standard loading conditions, and thus there is need for an alternative way to implement a cargo hold which is capable of safely withstanding the sloshing impact load even under partial loading.
In addition, in case of forming chamfers as above to reduce sloshing impact, the storage space in the cargo hold is relatively narrowed by the chamfers 31 and 32, and thereby the cargo hold may not be loaded with as much cargo as cargo holds in the same class.